This invention relates to a lockout system which is particularly useful on electrical control safety switches arranged on door-like closures which cover openings in fence-like enclosures that are used to guard electrically powered industrial equipment in order to restrict access to such equipment.
Safety switches are frequently used on door-like closures in factories so that when the closures are opened, the electrical power supply to the enclosed equipment is interrupted and remains interrupted until the closures are returned to their closed positions. Thus, workmen entering an enclosed area to maintain or to service or to otherwise contact the enclosed equipment are protected against movement of the equipment or electrical shocks while they are within the enclosure or guarded area.
A problem encountered is that if the closure is inadequately or accidentally closed, the switch on the closure may be inadvertently activated and complete the safety circuit to the equipment allowing equipment to operate in an unsafe manner. Hence, the invention herein relates to a lockout system which prevents an open closure from being inadvertently closed so that the door switch is inadvertently activated when someone is within the enclosure. The lockout system prevents the safety switch from completing the safety circuit when the door is opened and prevents the door from being unintentionally closed.
In more detail, the use of walls or fences or other restraining barriers around equipment within a factory is common. Particularly where robots or other electrically powered equipment are used, it is common to erect a protective fence or wall or other enclosure around the equipment. The electrical power supplied to the equipment, as a safety measure, may be interrupted whenever a door-like closure is opened so that someone may enter the enclosure and contact the equipment without fear of hazardous motion or of electrical shocks. However, there remains a possibility that someone may inadvertently close the door or that the door may otherwise swing shut when a workman is within the enclosure and does not want to have the electrical current actuated or the equipment in operation or any type of motion by the equipment.
The term door is intended here to encompass closures, such as doors, hatches, gates, etc., whether of a swinging or sliding type, which is used to close an opening in some sort of wall or fence or other restraining barrier. Thus, the term “door” is used in a generic sense herein.
A common type of electrical safety switch for such doors may be formed with two components, one mounted on the edge of a door and the other mounted on the frame or edge of the opening which the door normally closes. The two components cooperate to control the flow of power to equipment or other power using paraphernalia. Such two-part or two-component switches may be operated to allow current flow by having cooperating sensing devices which sense or signal when the two components are aligned and are closely adjacent. Conversely, when the two components are not aligned and/or are spaced apart widely, the switch is deactivated and interferes with the flow of current. Thus, sensing devices, for example, may be in the form of photoelectric cells, or magnetic sensors, or radio signals, or induction sensors or mechanical contacts, or key lock devices, or the like.
For practical use, the sensors that are used should operate to control or switch on the flow of current when the sensors are properly aligned and the door is closed relative to the door frame or the edge of the opening and, conversely, to switch off to prevent the flow of current when that condition is not present. Thus, the lockout system is intended to normally assist in locking the door in its closed position and, conversely, to prevent the door from closing after it is opened until someone manually operates the lockout system to again close the door. Hence, unless the door lockout system is manually and deliberately operated, the door will not close and, accordingly, the switch components will not be properly aligned so that electrical current flow to the enclosed equipment is prevented. The lockout system preferably includes an arrangement whereby the workmen must manually unlock the door to open the door, and once the door is open, the system prevents the door from closing until a deliberate manual act is performed. Hence, the lockout system will automatically keep the door from closing until it is deliberately intended to be closed.
The lockout system provides a simple, inexpensive construction which may be installed on pre-existing enclosures.
Thus, it is intended to be “fool proof” so that it may not be accidentally or inadvertently deactivated when the door is in open position. Consequently the system prevents the accidental flow of electrical current to enclosed electrically powered equipment when the door to the enclosure is not deliberately closed.